A voltage regulator uses a reference current source and a power supply voltage (battery) in order to deliver a regulated output voltage, in other words a voltage that is independent of the variations in the power supply voltage and of the variations in load, i.e. in the current drawn.
LDO voltage regulators are particularly suitable where there are small variations in the power supply voltage. For stability, LDO voltage regulators can be connected to an external capacitor mounted in parallel with the load to be supplied by the regulated voltage. When the LDO voltage regulator is turned on, the external capacitor is generally charged up by a relatively high charge current.
Now, this charge current may cause a voltage drop across the power supply battery, especially where several voltage regulators are connected together across the same power supply battery. Presently, the charge current is limited by generating a current that is the image of the charge current, then comparing this image current with a reference current. However, the limit must be high enough so as not to interfere with the operation of the voltage regulator. This drawback is accentuated by the fact that the image current is not very precise.
Furthermore, if the start-up of each voltage regulator is to be staggered in order to prevent the drop in voltage of the power supply battery, it then becomes necessary to study in detail the whole circuit in order to precisely define the order in which the various regulators are to be turned on. In addition, the interconnections between the various loads may lead to the appearance of interference-causing currents due to conducting parasitic diodes associated with the various levels of the output voltages of the various regulators during their start-up phase.
Accordingly, what is needed is a method and system to overcome the problems encountered in the prior art and to provide a method and system to prevent a voltage drop across a power supply during startup.